The present invention relates generally to the field of post chemical-mechanical polishing (post-CMP) cleaning operations, and more specifically to post-CMP cleaning solutions for copper-containing microelectronic substrates.
The present day fabrication of semiconductor devices is a complex, multi-step process. The Chemical-Mechanical Polishing (CMP) process is now a well-established enabling technology used by most advanced semiconductor operations for planarization of various substrates for production of devices with design geometries of less than 0.35 micron.
The CMP processes involve holding and rotating a thin, flat substrate of the semiconductor material against a wetted polishing surface under controlled chemical, pressure and temperature conditions. A chemical slurry containing a polishing agent, such as alumina or silica, is used as the abrasive material. In addition, the chemical slurry contains selected chemicals, which etch various surfaces of the substrate during processing. The combination of mechanical and chemical removal of material during polishing results in superior planarization of the surface.
The CMP process, however, leaves contamination on the surfaces of the semiconductor substrate. This contamination is comprised of abrasive particles from the polishing slurry, which may consist of alumina or silica with reactive chemicals added to the polishing slurry. In addition, the contaminant layer may comprise reaction products of the polishing slurry and the polished surfaces. It is necessary to remove the contamination prior to subsequent processing of the semiconductor substrate in order to avoid degradation in device reliability and to avoid the introduction of defects which reduce the manufacturing process yield. Thus, post-CMP cleaning solutions have been developed to cleanse the substrate surface of CMP residuum.
Alkaline solutions based on ammonium hydroxide have been traditionally used in post-CMP cleaning applications. To date, most CMP applications have been directed to aluminum, tungsten, tantalum, and oxide-containing surfaces.
However, copper is increasingly becoming a material of choice in the production of interconnects in semiconductor fabrication. Copper is replacing aluminum as the metal of choice in such fabrication. Conventional post-CMP processes are inadequate for cleaning surfaces containing copper. Copper, copper residue, and the slurry particles are the contaminants that exist on the copper and other exposed surfaces following this CMP process. The copper contamination diffuses quickly in silicon and silicon dioxide and other dielectric materials. Therefore, it must be removed from all exposed surfaces including the backside of the wafer to prevent device failure.
Post-CMP cleaning solutions that are traditionally effective on alumina and silica-based CMP processes are not effective on copper-containing surfaces. Copper is easily damaged by these cleaning solutions. In addition, cleaning efficacy with the present post-CMP cleaning solutions has been proven unacceptable.
Nam, U.S. Pat. No. 5,863,344, discloses a cleaning solution for semiconductor devices containing tetramethyl ammonium hydroxide, acetic acid, and water. The solution preferably contains a volumetric ratio of acetic acid to tetramethyl ammonium hydroxide ranging from about 1 to about 50.
Ward, U.S. Pat. No. 5,597,420, discloses an aqueous stripping composition useful for cleaning organic and inorganic compounds from a substrate that will not corrode or dissolve metal circuitry in the substrate. The disclosed aqueous composition contains preferably 70 to 95 wt % monoethanolamine and a corrosion inhibitor at about 5 wt % such as catechol, pyrogallol or gallic acid.
Ward, U.S. Pat. No. 5,709,756, discloses a cleaning composition containing about 25 to 48 wt % hydroxylamine, 1 to 20 wt % ammonium fluoride, and water. The pH of the solution is greater that 8. The solution may further contain a corrosion inhibitor such as gallic acid, catechol, or pyrogallol.
Hardi et al., U.S. Pat. No. 5,466,389, discloses an aqueous alkaline cleaning solution for cleaning microelectronic substrates. The cleaning solution contains a metal ion-free alkaline component such as a quaternary ammonium hydroxide (up to 25 wt %), a nonionic surfactant (up to 5 wt %), and a pH-adjusting component, such as acetic acid, to control the pH within the range of 8 to 10.
Schwartzkopf et al., European Patent No. 0647884A1 discloses photoresist strippers containing reducing agents to reduce metal corrosion. This patent teaches the use of ascorbic acid, gallic acid pyrogallol among others for the control of metal corrosion in alkali containing components.
U.S. Pat. No. 5,143,648 to Satoh et al., which is herein incorporated by reference, discloses novel ascorbic acid derivatives as antioxidants.
There is a need for a post-CMP cleaning composition for copper-containing surfaces. Such a post-CMP cleaning composition must effectuate substantial particle removal from the target surface and prevent corrosion of the copper-containing substrate. Such a post-CMP cleaning composition must also refrain from attacking the process equipment used in the post-CMP process. Such a post-CMP cleaning composition should also be economical, work effectively through a wide temperature range. Such a post-CMP cleaning composition should also be useful in cleaning utilizing alumina or silica-based slurries.
According to the present invention aqueous cleaning solutions for cleaning copper containing micro electronic substrates consist of a quaternary ammonium hydroxide, a polar organic amine, a corrosion inhibitor and deionized water.
Ascorbic acid by a wide margin is the most effective corrosion inhibitor when used in an alkaline solution for cleaning copper containing microelectronic substrates. We have found that addition of an organic acid, e.g. gallic acid to these compositions can improve the cleaning properties without sacrificing the effectiveness of the ascorbic acid as a corrosion inhibitor. Thus in some applications users may desire an addition of gallic acid to the cleaning composition.
The present invention is a cleaning solution for cleaning copper-containing microelectronic substrates comprising a quaternary ammonium hydroxide selected from the group consisting of tetraalkylammonium hydroxide, where the alkyl contains C atoms numbered from 1 to 10, and combinations thereof; an organic amine selected from the group consisting of monoethanolamine, aminoethylethanolamine, N-methylaminoethanol, aminoethoxyethanol, diethanolamine, triethanolamine, C2-C5 alkanolamines, and combinations thereof, optionally an organic acid, e.g. gallic acid; and a corrosion inhibitor selected from the group consisting of ascorbic acid, L(+)-ascorbic acid, isoascorbic acid, ascorbic acid derivatives, catechol, pyrogallol, resorcinol, hydroquinone, benzotriazole, and combinations thereof. The alkalinity of the solution is greater than 0.073 milliequivalents base per gram.
According to the invention an effective cleaning solution for cleaning copper-containing microelectronic substrates comprises; a) tetramethylammonium hydroxide, b) monoethanolamine, c) gallic acid, d) ascorbic acid, and deionized water. The alkalinity of the solution is greater than 0.073 milliequivalents base per gram.
Preferably, tetramethylammonium hydroxide is in the cleaning solution in an amount in the range from about 0.15 wt % to about 1.25 wt %, monoethanolamine is in the solution in an amount in the range from about 0.2 wt % to about 2.25 wt %, gallic acid in an amount in the range from 0.1 wt % to about 0.4 wt %, and ascorbic acid is in the solution in an amount in the range from about 0.10 wt % to about 0.9 wt %, balance deionized water.
A concentrate composition for a cleaning solution for cleaning copper-containing microelectronic substrates is also provided. The concentrate composition comprises tetramethylammonium hydroxide in an amount in the range from about 1.8 wt % to about 12.4 wt %, monoethanolamine in an amount in the range from about 2.0 wt % to about 27.8 wt %, gallic acid in an amount in the range of 0 wt % to about 4.0 wt %, ascorbic acid in an amount in the range from about 1.0 wt % to about 10.9 wt %, and the balance deionized water. An effective cleaning solution can me be achieved by mixing from about 1.5 wt % to 12.5 wt % of the concentrate with with deionized water.